Labour Leave feared for the party's chances of office if Brexit supporters in Labour backyards reward the Tories for delivering Brexit.

Policy and research director Laura Bierer-Nielsen said: “The roots of the Labour Party lie within working class communities up and down the country whose historical identities are based around industries such as fishing, mining - and it's many of those people who voted to Leave in the 2016 referendum.

The Labour chief faces a tricky act balancing young pro-EU voters and traditional supporters who back Brexit (Image: Getty)

(Image: Getty Images Europe)

“They did so with the expectation that their vote would not only be respected by their country but by the party they consider to represent them.

“On a more pragmatic basis, Labour Brexiteers matter electorally; if the Labour Party wishes to be in power within the next decade they must begin to recognise that over three in 10 of their voters voted to Leave – and, more significantly, that 70% of Labour constituencies did so as well.”

Former MP Gisela Stuart highlighted Labour's catastrophic demise in Scotland, where it sank from 41 seats in 2010 to just one seat at the 2015 election.

“It is perfectly possible for a party that's deeply entrenched to be wiped out,” she said.

“We shouldn't forget our roots - the core constituencies where you had not many public sector workers, largely white population and no university – these are the kind of places which have always been our Labour seats, and these are the ones which we are in danger of losing.”

The 2016 referendum was the UK's biggest ever democratic exercise, with Leave triumphing by 52% to 48% (Image: AFP)

Labour's top team is largely drawn from north London: leader Mr Corbyn is MP for Islington North; Shadow Foreign Secretary Emily Thornberry, MP for Islington South and Finsbury; Shadow Brexit Secretary Sir Keir Starmer, MP for Holborn and St Pancras; and Home Secretary Diane Abbott, MP for Hackney.

Ms Stuart believed the “narrative” presented by the party hierarchy threatened “core” seats.

“The reason we are in danger of losing them is twofold – it is on the one hand the current Labour narrative which goes out, which is very north Islington-based; I'm sorry but once you're north of the M25 that is not what they want to hear from their Labour Party,” said Ms Stuart, who represented Birmingham Edgbaston for 20 years.

Gisela Stuart campaigned to quit the bloc (Image: Daily Mirror)

Ms Stuart and Boris Johnson fought to leave the EU (Image: Sky News)

“The second one is we have allowed Labour Leavers in particular to be demonised; the kind of language which comes out – 'they're all old, they didn't know any better because they're weren't terribly bright, and they're all racist'.”

Ms Stuart, who chaired the official Vote Leave campaign, rubbished claims Leave voters had changed their minds since June 2016.

Dismissing last month's 670,000-strong Remainers' march on Westminster demanding another poll, she said: “How many there were there who said, 'I voted Leave and now I have changed my mind'?”

Remainers took to the streets demanding a second referendum (Image: Getty Images)

Speaking at the central London event, Ms Hoey admitted Brexiteers “took our eyes off the ball” in the aftermath of their 2016 triumph - but urged Labour Leavers “to keep the faith”.

And she praised party chief for sticking to Brexit, as promised in the 2017 manifesto.

Mr Corbyn was a leading Eurosceptic for 32 years on the Commons backbenches before discovering a newfound enthusiasm for the EU after winning the party leadership in 2015.

“We know that Jeremy has been solidly critical of the EU for many, many years,” said Ms Hoey.

Kate Hoey warned of the dangers for Labour if it wasn't seen to be supporting Brexit (Image: Newcastle Chronicle)

“When he became leader he was in a slightly more difficult position, particularly as the party had decided that they were in favour of Remain.

“But if I was to conjecture, which we can only do unless you're talking to him personally, I would be very confident that he wants to Leave the EU.”

Mr Corbyn's office pointed to statements he has made previously about voting Remain and respecting the referendum result.

Labour donor John Mills, the millionaire shopping channel tycoon, feared for the party in heartlands outside London.

John Mills believes the party faces difficulties in traditional heartlands (Image: Ben Pruchnie/Getty)

The 2017 snap election saw Labour claim seats in the capital with landslide majorities – some of more than 30,000 - but surrender constituencies like Mansfield and Stoke-on-Trent South to the Conservatives.

“Labour is not going to win the next general election by piling up huge majorities in London,” warned Mr Mills.

“It's going to win the next election by winning marginal seats in places like Wales, and the Midlands and the North – and if we carry on the way we are, we're not going to do that.”